Voltage regulators are widely used in modern electronic systems for a variety of applications such as computing (server and mobile) and POLs (Point-of-Load Systems) for telecommunications because of their high efficiency and small amount of area/volume consumed by such converters. Widely accepted voltage regulator topologies include buck, boost, buck-boost, forward, flyback, half-bridge, full-bridge, and SEPIC topologies. Multiphase buck converters are particularly well suited for providing high current at low voltages needed by high-performance integrated circuits such as microprocessors, graphics processors, and network processors. Buck converters are implemented with active components such as a pulse width modulation (PWM) controller IC (integrated circuit), driver circuitry, one or more phases including power MOSFETs (metal-oxide-semiconductor field-effect transistors), and passive components such as inductors, transformers or coupled inductors, capacitors, and resistors. Multiple phases (power stages) can be connected in parallel to the load through respective inductors to meet high output current requirements.
Voltage regulators ideally have high efficiency under all load conditions, including light load, and low power loss when the regulator is off. High power voltage regulators often employ separate controllers and power stages. For example, high power DC-DC voltage regulators typically have a single phase (power stage) or multiple phases e.g. in the case of multiphase buck converters. The power stages of a voltage regulator can be discrete (separate driver and power switch packages) or integrated (one package contains driver and power switches). Integrated power stages include advanced circuitry such as internal supply rails, bootstrap supply, integrated current sense, integrated temperature sense, etc. Light load conditions result in periods where the power stage has little or no activity. Multiphase converters typically have the ability to drop phases, where one or more phases are not actively switching and not supporting any of the additional current. In addition, for extremely light load currents, phases may be operating in pulse frequency mode, where a substantial amount of time passes between switch cycles in which the power stage is not switching. Thus, DC-DC voltage regulators have multiple operating modes where having one or more power stages in sleep mode is desirable to reduce power loss. The delay associated with exiting sleep mode is an important performance parameter for the power stage, in certain cases some exit delay is acceptable, and in other cases the power stage must immediately respond to changes in its input.
Some conventional DC-DC voltage regulators forgo the complexities associated with implementing power stage sleep mode, and therefore do not offer this feature. For these regulators some internal circuitry that could otherwise be disabled remains on in the power stage, unnecessarily increasing power dissipation of the voltage regulator. Other conventional DC-DC voltage regulators provide a dedicated pin for indicating when the power stage should enter sleep mode. This approach requires the controller and each power stage (phase) of the voltage regulator to have an extra pin/signal for enabling this feature, increasing the system size and cost. Also, voltage regulation is conventionally disabled in sleep mode which requires high latency for the power stage to resume normal voltage regulation upon exiting the sleep mode. Also, conventional sleep mode implementations do not optimize pulse frequency and phase drop modes of operation relative to power stage power dissipation.